The present disclosure relates generally to processes for initiating Fischer-Tropsch synthesis. In particular, the application concerns a process for the initiation of Fischer-Tropsch synthesis, the process comprising: (i) providing the reaction zone with a temperature of no more than 140 C.; then (ii) purging the reaction zone with a purge gas comprising N.sub.2 at a pressure in the range of 2 barg to 10 barg; then (iii) contacting the catalyst in the reaction zone with a gaseous reaction mixture comprising H.sub.2 and CO in a ratio of between 1:1 and 3:1 at a pressure of no more than 20 barg and at a temperature of no more than 140 C.; then (iv) heating the reaction zone to a temperature of at least 200 C.; and (v) pressurizing the reaction zone to a pressure in the range of 30 barg and 45 barg.

A process for preparing C.sub.2 to C.sub.4 hydrocarbons includes introducing a feed stream into a reaction zone of a reactor, the feed stream comprising hydrogen gas and carbon monoxide. An additional stream is introduced into the reaction zone of the reactor, the additional stream comprising carbon dioxide. A combined stream that includes the feed stream and the additional stream is converted into a product stream comprising C.sub.2 to C.sub.4 hydrocarbons in the reaction zone in the presence of a hybrid catalyst. The hybrid catalyst includes a mixed metal oxide catalyst component, and a microporous catalyst component. The process operates at a gas hourly space velocity in excess of 2500 hr.sup.1 and effectively yields a net carbon dioxide selectivity of less than 5.0% and a productivity of C.sub.2-C.sub.4 hydrocarbons greater than 75 g hydrocarbons per kilogram of catalyst per hour.

A method is described for shutting down a Fischer-Tropsch reactor fed with a reactant gas mixture comprising a synthesis gas and a recycle gas recovered from the Fischer-Tropsch reactor in a synthesis loop, said Fischer-Tropsch reactor containing a Fischer-Tropsch catalyst cooled indirectly by a coolant under pressure, comprising the steps of: (a) depressurising the coolant to cool the reactant gas mixture to quench Fischer-Tropsch reactions taking place in the Fischer-Tropsch reactor, (b) stopping the synthesis gas feed to the Fischer-Tropsch reactor, and (c) maintaining circulation of the recycle gas through the Fischer-Tropsch reactor during steps (a) and (b) to remove heat from the Fischer-Tropsch reactor. The method safely facilitates a more rapid return to operating conditions than a full shut-down.